Organic thin-film transistors (OTFTs) have recently gained a lot of interest as building blocks for printable electronic applications that can greatly benefit from low-cost, large-area fabrication and flexible form factors, such as radio-frequency identification tags (RFID), drivers for electronic paper, driving circuits for flat panel displays (FPDs), and flexible analog circuits for power management. To achieve high performance OTFTs, development of suitable gate dielectric materials in addition to high-mobility organic semiconductors is important. Preferably, gate dielectric materials should have a high dielectric constant κ, should have low leakage current, high dielectric strength, and should be processible into thin, high-quality, low-defect films to form OTFTs with a reduced operating voltage and large on/off ratio. Inorganic metal oxide dielectrics (10<κ<300) have been used as gate insulators to reduce transistor operation voltage. However, the processing of these materials, such as by e-beam deposition, RF sputtering, pulsed laser deposition (PLD) and plasma enhanced chemical vapor deposition (PECVD), requires both high vacuum and high temperature conditions. Although anodization can be used to deposit some metal oxides, such as TiO2 and Al2O3, on flexible organic electronics, the patterning of the metal oxides is difficult since most oxides are very resistant to etching. On the other hand, polymeric insulators, which can be easily processed using spin coating, casting, and inkjet printing, generally possess a low K ranging from 2 to 4.
Certain thin-film dielectric materials have been investigated for use in OTFTs; in attempts to combine the high dielectric constants, the ability to form very thin films, low leakage current, high dielectric strength, processibility, and low cost of fabrication. However, in known OTFTs based on nanocomposite gate insulators, success in achieving the desired device properties by mixing high-dielectric ceramic powders with polymers has been limited by the high viscosity of ceramic/polymer mixtures and by ceramic particle coagulation and/or low solubility of the ceramic materials, typically resulting in unacceptable film quality, and leading to dielectric composites with low electric-field breakdown strength, high dielectric loss, and devices with poor electrical characteristics.
Therefore, despite conventional materials known to those of ordinary skill in the art, there remains a need for printable gate insulators with high dielectric constant for incorporation into OTFTs having other desirable electrical properties.